Process for the production of hydrogen by microorganisms

ABSTRACT

The present invention relates to a process for the production of hydrogen comprising treating in an anaerobic condition a substrate such as waste water including organic matter using sludge compost, whereby stable hydrogen generation at a higher efficiency for a longer period of time is attained together with the treatment of waste water.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Hydrogen is clean energy that does not discharge carbon dioxide evenafter its combustion, and additionally, its exothermic energy per unitweight is three fold higher than that of petroleum.

Also, hydrogen may be modified into a form of electric energy by itssupply into fuel cells.

The present invention relates to a process for the production ofhydrogen during the process of treating a variety of substrates, forexample, waste water containing highly concentrated organic matter, byusing an anaerobic microflora (a group of microorganisms), whereby thepresent invention serves for the treatment of waste water and hydrogengeneration. Therefore, the present invention not only plays an importantrole in generating hydrogen for the energy industries but also plays animportant role industrially for waste water treatment and pollutionmanagement.

2. Prior Art

Hydrogen is currently produced by thermal naphtha decomposition or bywater electrolysis. Because these processes consume fossil fuel,however, they generally do not serve for improving the globalenvironment. It is also expected that the consumption of fossil fuelwill be reduced in the future.

Alternatively, hydrogen generation using microorganisms is grouped intotwo types; (1) a process employing a photosynthetic microorganism and;(2) a process employing an anaerobic microorganism. The former process,which depends on photosynthetic energy may be complex and inefficient aswell as costly. Additionally, the hydrogen generation rate by suchmicroorganisms is slow. Furthermore, the substrate for hydrogengeneration is limited. Thus, the former process has a great number ofproblems, and has not yet been applied in practice (see YoshimasaTakahara, "Microorganisms contributing to industrialdevelopment--Principal role in biotechnology" Hakua Shobo, publishedDec. 25, 1983, p. 182-185).

Hydrogen generation by means of anaerobic microorganisms is classifiedin either the process using a microflora such as digested sludge andlumen bacteria or the process using pure cultures of bacteria; thelatter process for waste water treatment is far from reaching apractical stage, because the range of substrate is limited and theprocess requires sterile conditions, and the like.

On the other hand, in the process which uses a microflora (a mixedpopulation of microorganisms), the microflora can be adapted to a widevariety of substrates without requiring sterile procedures; additionallyvarious waste waters may be used as substrates for hydrogen generation.

Although a number of reports have been published on hydrogen generationby anaerobic microfloras, many of the problems concerning hydrogenproductivity and stability are still unsolved.

Problems to be Solved by the Invention

Taking into account the current state of the art described above, thepresent invention has achieved the objective of developing a novelsystem capable of stably generating hydrogen at a higher efficiency fora long period of time as well as the objective of developing a novelsystem capable of treating various industrial wastes with a higherefficiency.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 depicts the process for generating hydrogen by microorganisms inaccordance with the present invention.

Means for Solving the Problems

A wide variety of investigations were done to attain the aboveobjectives and as a result the present invention was achieved. Thepresent invention is based on a fundamental technical concept of amethod for stably generating hydrogen at a higher efficiency for a longperiod of time using the microorganisms in sludge compost as microflora.

Any of the sludge compost produced by forcing aeration into sewagetreatment sludge and thereby rapidly preparing the sludge into compostis referred to as the sludge compost to be used in accordance with thepresent invention. Such sludge compost can be produced by any of avariety of methods; for example, when the water content of the wastewhich contains organic matter is adjusted by adding to the waste acarbon source, such as rice husks and sawdust if necessary, by furtheradding to the waste a part of a compost product if necessary, and byfeeding the resulting mixture into a fermenter from the top whileaerating the mixture from the bottom for compost preparation, crudecompost is produced. For continuous compost preparation, the rawmaterial feeding from the top and the recovery of crude compost from thebottom should be synchronized. During the compost preparation describedabove, the temperature is elevated so that hazardous pathogenic bacteriaare deactivated. As the sludge compost in accordance with the presentinvention, the crude compost drawn out from the fermenter may be used asis, or the crude compost may be prepared into a fully fermented compost,after post-fermentation such as open-air storage for one to severalmonths.

Whether the sludge compost is a crude compost or a fully fermentedcompost, the sludge compost thus prepared does not contain methaneproducing bacteria which are deactivated in contact with oxygen. Thus,while methane producing bacteria are deactivated in the presence ofoxygen, most hydrogen-generating anaerobic bacteria are not killed whenin contact with oxygen; as the hydrogen-generating bacteria arefacultative anaerobes or are spore-forming bacteria, these bacteria arestill alive even after contact with oxygen. Thus, hydrogen-generatingsurvive the contact with oxygen and are present in the compost. In otherwords, if waste water and other substrates are later treated underanaerobic conditions, hydrogen generation is exclusively facilitated bythe action of hydrogen generating bacteria with no occurrence of themethane fermentation which generally occurs during anaerobic treatmentof waste water. Therefore, in accordance with the present invention,hydrogen generation is realized at an exceedingly high efficiency.

So as to generate hydrogen in accordance with the present invention,waste water or other various substrates are brought sufficiently intocontact with the sludge compost in an anaerobic atmosphere to generatehydrogen which can then be collected. When waste water is used as thesubstrate, waste water treatment is carried out together with thegeneration of hydrogen, making the present invention extremely useful ina practical sense.

In order to practice the present invention as shown in FIG. 1 as anexample and without limitation, a substrate is charged into a fermenteror a bioreactor, followed by the addition of the sludge compost (0.01 to20% w/v, preferably at 0.5 to 5% w/v, without specific limitation). Ananaerobic atmosphere is obtained by following a routine method, such assealing the gas phase with N₂ gas or the like. The sludge compost thenis maintained at a temperature suitable for the growth thereof(generally at about 40° to 70° C., the temperature varying depending onthe type of the sludge compost), with the reaction progressing whilestirring if necessary.

As the reaction progresses, hydrogen is generated. While substratedecomposition is carried out, the hydrogen generated is recovered asenergy. When waste water is employed as the substrate for example, it istreated by the process to yield clean water.

Waste water discharged from manufacturing plants such as agriculturalplants, juice plants, food plants, chemical plants and the like, wastewater containing organic matter such as sewage water, urine and thelike, and artificial substrates routinely employed for the culture ofmicroorganisms and comprising a carbon source, a nitrogen source,minerals, vitamins etc. can be used as substrate. In order for hydrogengeneration and liquid waste treatment to proceed in a smooth fashion,appropriate dilution, mixing or the like, and addition of requiredcomponents may need to be done, for appropriate adjustment of thesesubstrates.

The present invention will now be explained in detail in the followingexamples.

EXAMPLE 1

A 1% w/v of sludge compost was added to an artificial liquid wastehaving a composition of 1.5 g KH₂ PO₄, 4.2 g Na₂ HPO₄.H₂ O, 0.5 g NH₄Cl, 0.18 g MgCl₂.6H₂ O, 5 g yeast extract, 10 g cellulose powder, and 1liter of distilled water, followed by sealing the gas phase with N₂ gas.The resulting mixture was maintained at 60° C. in an anaerobiccondition.

As a result, 73% of the cellulose powder in the artificial liquid wastewas decomposed and removed in 96 hours, with the generation of 1908 mlof hydrogen gas. The efficiency of hydrogen generation in the presentexample was 1.89 moles of hydrogen per mole of cellulose decomposed.

EXAMPLE 2

The artificial waste water as described in Example 1 was maintained atpH 6.5 for treatment under the same conditions. As a result, about 98%of the cellulose powder was decomposed in 120 hours, with the generationof 2613 ml of hydrogen gas.

EXAMPLE 3

For anaerobic treatment, the sludge compost was inoculated into wastewater from a food plant, which contains sugars as the major component ofits composition (TOC; 40,000 mg/l) and having been discharged at therate of 1 m³ /day. While maintained at pH 6.5, the resulting mixture wassubjected to continuous operation for a six day reaction period.

As a result, hydrogen gas was generated at a rate of 3.18 m³ /day over aperiod of 3 months. The removal rate of sugars contained in waste waterwas above 99%.

EXAMPLE 4

A 0.5% w/v sludge compost as microflora was inoculated into 3 liters ofa CT medium containing 1% cellulose powder (Product Name; Funacell SF)as a carbon source and then cultured under anaerobic conditions withagitation.

The following measurements were done over time: pH of the medium by theglass electrode method; VSS (insoluble organic substances) by the sewagewater testing method; lower C₂ to C₈ fatty acids by the gaschromatography FID method; TOC (total organic carbons) with a totalorganic carbon tester. The gas generated gas was quantitatively assayedby the substitution method on water using water below pH 3, and itscomposition was analyzed by the gas chromatography TCD method.

As a result, the cellulose in the medium was nearly solubilized andfermented during a 96-hour culture, with the generation of 9507 ml ofgas. The gas composition was as follows; hydrogen at 59% and carbondioxide gas at 41%. As the generation of the gas processed, the pH ofthe medium decreased from pH 6.82 to pH 4.78. The lower fatty acidsproduced were mainly acetic acid and lactic acid. These results indicatethat the generation of hydrogen possibly occurred during thefermentation to produce the mixture of acetic acid and lactic acid.

Effect of the Invention

The present invention relates to a method for generating hydrogen usingan organic substrate. As one of the embodiments, a method for generatinghydrogen during the process of treating waste water is described. Inconventional anaerobic waste water treatment, the hydrogen gas generatedis converted into methane by methane producing bacteria as a final stagein methane fermentation.

Provided that the anaerobic treatment is done using a microflora lackingin methane producing bacteria, waste water can be decomposed intohydrogen, carbon dioxide gas and organic acids without methanegeneration.

Because sludge compost that is rapidly prepared does not contain methaneproducing bacteria, the compost should be of a microflora suitable forrecovering hydrogen gas during the process of treating waste water.

As the first process to be drawn to such sludge compost, the presentinvention has successfully achieved stable hydrogen generation at a farhigher efficiency over a long period of time. Particularly, the effectcannot be estimated with respect to energy generation alone. If wastewater is used as a substrate for sludge compost, not only would hydrogenbe generated but the efficient treatment of waste water would also beachieved. Thus, the present invention is excellent as both a means forpollution control management and energy generation.

What is claimed is:
 1. A process for the microbial production ofhydrogen gas, comprising the steps of:(a) providing a sludge compostcontaining hydrogen-generating anaerobic bacteria and deactivatedmethane producing bacteria which has been prepared by forcing aerationinto a sewage treatment sludge; (b) contacting a liquid waste containingorganic matter with said sludge compost in an anaerobic atmosphere byadding about 0.01 to 20% w/v of said sludge compost to said liquid wasteto generate hydrogen gas; and (c) collecting said generated hydrogengas.
 2. The process according to claim 1, wherein said sludge compost instep (a) is a crude compost
 3. The process according to claim 1, whereinsaid sludge compost in step (a) is a fully fermented compost which hasbeen prepared by keeping a crude compost, formed from said sludgecompost, in open air storage for a period of about one to severalmonths.
 4. The process according to claim 1, wherein said step (b) ofcontacting said liquid waste with said sludge compost is maintained at atemperature in the range of about 40° C. to 70° C.
 5. The processaccording to claim 1, wherein said step (b) of contacting said liquidwaste with said sludge compost is carried out with stirring of saidliquid waste with said sludge compost.
 6. The process according to claim1, wherein said liquid waste is waste water.